There have been known audio systems including speakers installed in a vehicle seat (for example, see Patent Literatures 1 and 2). Such an audio system includes a full-range speaker installed near the headrest of the seat and subwoofers installed in the backrest or seat surface of the seat and is able to output sounds in a low-to-high wide frequency range. The subwoofers are embedded in the seat and configured to vibrate the seat in accordance with the level of a low-frequency-band music signal. When a sound outputted from the full-range speaker installed near the headrest and vibrations outputted from the subwoofers are combined together, the realism can be enhanced.
Subwoofers are not used solely to enhance the realism of music by outputting deep bass (low-frequency sounds). They have been also used recently as means for notifying the driver (alarm means).
For example, there have been proposed vehicle notification devices that when the vehicle crosses a lane marking, notify the driver that the vehicle has crossed the lane marking through vibrations, as well as notify the driver of the position of the crossed lane marking using the vibration position of the seat (for example, see Patent Literature 3). There has been also proposed a vehicle notification device determines whether the driver is dozing by detecting the heart rate of the driver using a heart rate monitor and awakens the driver by vibrating a vibrator (exciter) disposed in a seat (see Patent Literature 4).
As seen above, an alarm or notification can be issued to the driver by vibrating a vibrator (subwoofer, etc.) disposed in the driver's seat when necessary. There have been also proposed many other methods of notifying the driver by vibrating speakers or the like installed in the driver's seat.